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The recovery ratio of longwall top coal caving (LTCC) technology is an important measure of its effectiveness. However, the recovery ratio of single-opening sequential caving technology in thick and extra-thick coal seams needs improvement. To address this, an independent cluster-group caving technology is proposed in this study. Four numerical simulation experiments were conducted to compare the recovery ratio and drawing balance of four-opening independent cluster-group caving technology and single-opening sequential caving technology. Results show that the recovery ratio in four-opening independent cluster-group caving technology is approximately 6% higher than in single-opening sequential caving technology when the thickness of the broken gangue layer and the coal seam are the same. Additionally, a judgment formula for the broken immediate roof thickness is provided when the top coal recovery ratio is seriously affected. The independent cluster-group caving technology demonstrates stronger stability and better adaptability under different conditions, as its caving sequence can prevent larger thickness changes and gangue disturbances during the drawing process. Overall, this study highlights the potential of independent cluster-group caving technology to improve the recovery ratio of LTCC technology in thick and extra-thick coal seams. [ABSTRACT FROM AUTHOR]

Drawing support is one of the unique equipment for longwall top coal caving (LTCC) technology in coal mine, whose structure has a significant effect on the top coal drawing mechanism. This research systemically investigates the effect of the dip angle of shield beam (α), length ratio of shield beam to tail beam (RL), and rotation angle of tail beam (β) on the top coal recovery, drawing body and top coal boundary by using particle flow code (PFC2D). The results show that the variation of α and β has a greater effect on the top coal drawing mechanism, the ideal α should be about 55°, RL is within the range of 0.8–1.0, and the tail beam rotates at a small angle range, which is beneficial to the top coal drawing in the panel. When α is large while RL is small, the volume of the initial drawing body gradually increases. With the increase of drawing height, volumes of drawing body under different β all plot an increasing trend with an incremental growth ratio. With increasing RL, the initial top coal boundary on the goaf side experiences the change of “upward concave-nearly linear-upward concave”, while that on the support side shows a curve with a fast-changing slope and closes to the vertical central line of drawing opening. The research results have important theoretical and field guiding significance for the selection and design of hydraulic support in LTCC. [ABSTRACT FROM AUTHOR]